U.S. Pat No. 4,693,567 to Yasuto Ozaki disclosed an apparatus for projecting luminous lines on an object by a laser beam. Reviewing FIG. 5 of this prior art, a horizontal and a vertical line is projected to an object for marking purpose. However, it lacks of any angle-variation mechanism for optionally changing the angles of the projecting laser lines, thereby limiting its utility or function.
The present inventor has found this fact and invented the present optical marking apparatus for varying marking angles.